Cylindrical candle filter elements are used in the filtration of gasses containing entrained particulate matter. Those cylindrical candle filter elements include a tubular porous ceramic filter having a hollow interior closed at one end and having an annular radial flange at the opposing end. In practice, a plurality of cylindrical candle filter elements are mounted through counterbored apertures on a tube sheet which is suspended across the hollow width of a cylindrical chemical or filtration vessel. In practice, the annular flange fits into the enlarged counterbored portion of the tube sheet mounting aperture and the smaller aperture itself is slightly larger than the outer diameter of the cylindrical portion of the candle filter element.
Such candle filter elements are shown and described in U.S. Pat. No. 4,968,467 and are not as brittle and fragile as earlier known types of ceramic filter elements. It includes a ceramic skeletal base consisting of randomly disposed ceramic fibers bonded together at their intersections with the interstices filled or partly filled with ceramic particles which are bonded to one another and to the skeletal base to form a unitary elongate tubular filter element open at the flanged end and closed at the other end.
Additionally, in U.S. Pat. No. 5,238,478, a candle filter element and a method of making same are disclosed wherein the flange end of the candle filter element and the closed end of the filter element are immersed in a colloidal bath and later dried at a temperature of about 600 degrees Fahrenheit to bond the particles in the colloidal bath to the candle. In this process, the ends of the candle were densified to at least about twice the density of the untreated intermediate filter section. In the aforementioned '478 patent, it was believed that the intermediate portion (non-dipped portion of the candle) extends from a short distance of about 11/2 inches or less from the end wall to a short distance of about 11/2 inches from the flange with the understanding that these distances were not critical but may vary with the size and strength of the candle.
It is an object of the present invention, generally stated, to provide a new and improved cylindrical candle filter element having an improved flange portion which provides for added use-life of the candle filter.